Asp.net Mvc - Regex For Extracting Second Level Domain From FQDN?

I need to extract the second level domain from a FQDN. For example, all of these need to return "[url]....

Here's what I have so far:

Dim host = Request.Headers("Host")
Dim pattern As String = "(?<hostname>(w+)).(?<domainname>(w+.w+))"
Dim theMatch = Regex.Match(host, pattern)
ViewData("Message") = "Domain is: " + theMatch.Groups("domainname").ToString

It fails for example.com:8080 and bar.foo.example.com:8080.